1. Field of the Invention
The present invention pertains to methods and apparatuses for growing single-crystals of silicon by the Czochralski technique, and in particular, to improvements to effectively prevent oxidation induced stacking fault (OSF) formation.
2. Prior Art
High temperature heat treatments in the semiconductor device process sometimes generate OSF in CZ (Czochralski) silicon wafers. OSF in the electronically active layer near the surface could induce device failures by causing current leakage and result in a shortened lifetime of carrier.
The supersaturated oxygen in the single-crystals has hitherto been considered to be responsible for OSF formation. More specifically, when CZ single-crystals are subjected to high temperature heat treatments, oxygen atoms produce miniscule SiO.sub.2 precipitates. As the oxygen precipitate enlarges, it produces interstitial silicon which has been supposed to induce a secondary defect such as OSF.
The inventors have previously proposed a method of growing silicon single-crystals which can prevent the formation of the oxygen precipitates, as disclosed in Japanese Patent Application A-Publication No. 61-201692. The method comprises the steps of providing a temperature control device at a prescribed range of the silicon single-crystal during pulling, and holding the entire single-crystal at a temperature range of between 1,100.degree. and 900.degree. C. for a period of at least three hours, and its object has been to prevent the formation of oxygen precipitates, thereby reducing OSF formation during high temperature heat treatments in the semiconductor device process.
However, after a further investigation, the inventors have found that the above-mentioned method definitely prevents the formation of the oxygen precipitates, but causes an increase in the OSF densities after high temperature treatments.